Some internal combustion engines include engine control systems that deactivate one or more cylinders under low load situations. For example, an eight cylinder engine can be operated using four cylinders to improve fuel economy by reducing pumping losses. This process is generally referred to as displacement on demand (DOD) or cylinder deactivation.
Electric hybrid vehicles include an engine and at least one electric machine. The electric machine draws current from the battery and powers the vehicle alone or in combination with the engine. During braking, the electric machine operates in a generator mode and assists braking by absorbing kinetic energy of the vehicle to slow vehicle motion. The generator converts the absorbed kinetic energy to current, which is used to recharge the battery. This process is commonly referred to regenerative braking.
In a hybrid vehicle, regenerative braking can be implemented when the vehicle is powered by the engine and/or the electric motor at the time of braking. However, during periods when the vehicle is driven by the engine, current that is produced by regenerative braking has been limited by engine braking. In other words, the engine slows the vehicle by absorbing some of the kinetic energy of the vehicle. As a result, less kinetic energy is absorbed through the regenerative braking, which reduces current generation.